Sorry to let you know but demon slayer marks can be unlocked by others too just like mitsuri in the same season, now I think I'll stop watching your videos.
(idea) tengen could have a blood demon art of making sounds that are so loud that the demon slayer fighting him would have their ears burst and there body would go crazy cuz of how loud it is)
i have a theory. theory: remember in mugan train enmu made tanjiro inside a dream but maybe he did not wake up and rengoku did not die so at the end of demon slayer enmu would be like "wake up tanjiro" and it would be a huge plot twist.
Imagine if mukago(the lower moon demon with two horns, idk if I spelled the name right), had plant bda, and could grow any plant just by description.. It doesn’t make sense? What if so it’s just flowers right, technically Muzan could get blue spider lily with her help